A new target for synthesis of sandwiched beryllium, magnesium, and calcium dimers: C5H7-M-M-C5H7 and C4H4P-M-M-C4H4P

Group 2 bis-element sandwiches formed by homoleptic open sandwiches with formula C₅H₇-M-M-C₅H₇ and C₄H₄P-M-M-C₄H₄P (M = Be, Mg, and Ca) have been studied at the B3LYP/cc-PVDZ and BP86/6-311G(d,p) levels of theory. The predicted M-M bond distances are much shorter than in the equivalent isolated M-M dimer and indicate substantial Be-Be, Mg-Mg, and Ca-Ca bonding. An NBO analysis shows that each M-M unit contains a single covalent bond and that the unit is linked to the open pentadienyl and phospholyl ring via ionic bonds. We thus predict that these new compounds are viable synthetic targets.     

Synthesis, characterization and comparison of group 14 pyrrolides and indolides Ph3MX (M = Si, Ge, Sn; X = C4H4N, C8H6N)

The biologically important heterocycles pyrrole, C₄H₄N, and indole, C₈H₆N, ought to be useful as reagents in organic synthesis. Unfortunately, working with them has proved to be difficult because they tend to self-polymerize in solution, especially in the presence of acid catalysts. When the self-polymerization can be controlled, however, the pyrrole and indole units should provide an important route to selective N-metal binding, particularly when these ligands are activated by alkyl-lithium reagents. Using this approach, a general synthesis of the group 14 pyrrolides and indolides, Ph₃MX (M = Si, Ge, Sn; X = C₄H₄N, C₈H₆N), has been developed and the results are reported here. The compounds are formed as high-melting, white crystalline solids and have been characterized by ¹³C-, ²⁹Si- and ¹¹⁹Sn-NMR, Raman and electron-impact mass spectroscopy as well as elemental analysis. A single-crystal X-ray study of Ph₃Si(C₄H₄N) has shown that the compound is disordered in the tetragonal lattice, even at low temperature (100 K).     

Etude vibrationnelle des composes (C4H4P)Mn(CO)3 et [C4H2(CH3)2P]Mn(CO)3 et calcul du champ de force du cycle C4H4P complexe

The Raman and infrared spectra (4000200 cm^?1) of (C₄H₄P)Mn(CO)₃ and (C₄D₄P)Mn(CO)₃, and of [C₄H₂(CH₃)₂P]Mn(CO)₃ and [C₄D₂(CH₃)₂P]Mn(CO)₃ in the liquid and solid states (10–400 K) have been investigated. A complete vibrational assignment is proposed and valence force fields of the (C₅H₅) and (C₄H₄P) cycles are compared. From these results, it is clearly shown that the (C₄H₄P) rings are more electrophilic and weaker π-electron donors than (C₅H₅) rings, this is in agreement with their chemical behavior.     

Singlet-triplet energy separation in divalent seven-membered cyclic conjugated compounds C6H6C, C6H6Si, C6H6Ge, C6H6Sn, and C6H6Pb

The electronic and thermal energy differences, ΔE(t-s); enthalpy differences, ΔH(t-s); and free energy differences between the singlet and triplet states, ΔG(t-s), were calculated for C₆H₆C, C₆H₆Si, C₆H₆Ge, C₆H₆Sn, and C₆H₆Pb at the B3LYP/6-311++G (3df, 2p) level. The singlet-triplet splitting, G _s-t, of C₆H₆C, C₆H₆Si, C₆H₆Ge, C₆H₆Sn, and C₆H₆Pb generally increased from C₆H₆C toward C₆H₆Pb. The most stable tautomers and conformers were suggested for the singlet and triplet states of C₆H₆M (M = C, Si, Ge, Sn and Pb). The geometrical parameters were calculated and discussed. The text was submitted by the authors in English.     

Vapour-liquid equilibrium data for the systems C2H6 + N2, C2H4 + N2, C3H8 + N2, and C3H6 + N2

High pressure vapour-liquid equilibrium data for the C₂H₆ + N₂, C₂H₄ + N₂, C₃H₈ + N₂, and C₃H₆ + N₂ systems are presented. The data are obtained isothermally in the range from 200 K to 290 K. For each point of data, temperature, pressure and liquid and vapour phase mole fractions are measured.Values for the vapour phase mole fractions are calculated from the obtained pressure, temperature and liquid phase mole fractions. The calculated values are compared with the experimental results, and it is found that the average mean deviation between calculated and experimental mole fractions is less than 0.009 for the systems considered in this work.     

Reactions of the dications C7H6, C7H7, and C7H8 with methane: Predominance of doubly charged intermediates

The reactions of methane with the dications C₇H₆²⁺, C₇H₇²⁺, and C₇H₈²⁺ generated by electron ionization of toluene are studied using mass-spectrometry tools. It is shown that the reactivity is dominated by the formation of doubly charged intermediates, which can either eliminate molecular hydrogen to yield doubly charged products or undergo charge-separation reactions leading to the formation of a methyl cation and the corresponding C₇H_n+1⁺ monocation. Typical processes observed for dications, like electron transfer or proton transfer, are largely suppressed. The theoretically derived mechanism of the reaction between C₇H₆²⁺ and CH₄ indicates that the formation of the doubly charged intermediate is kinetically preferred at low internal energies of the reactants. In agreement, the experimental results show a pronounced hydrogen scrambling and dominant formation of the doubly charged products at low collision energies, whereas direct hydride transfer prevails at larger collision energies.     

Multiconfiguration self-consistent wavefunctions for CH4, C2H4 and C2H6

The results of several MC SCF calculations on CH₄, C₂H₄ and C₂H₆ with minimun bases of Slater type AO's are reported. The computing method is a quadratically convergent process. Better final energies are obtained if localized MO's are used.     

Synthesis and crystal structure of Ir(C2H4)2(C5H7O2)

We report a new synthesis and characterization of Ir(C₂H₄)₂(C₅H₇O₂) [(acetylacetonato)-bis(η²-ethene)iridium(I)], prepared from (NH₄)₃IrCl₆ · H₂O in a yield of about 45%. The compound has been characterized by X-ray diffraction crystallography, infrared, Raman, and NMR spectroscopies and calculations at the level of density functional theory. Ir(C₂H₄)₂(C₅H₇O₂) is isostructural with Rh(C₂H₄)₂(C₅H₇O₂), but there is a substantial difference in the ethylene binding energies, with Ir-ethylene having a stronger interaction than Rh-ethylene; two ethylenes are bound to Ir with a binding energy of 94 kcal/mol and to Rh with a binding energy of 70 kcal/mol.     

Electron scattering differential cross sections for C2H2, C2H4, and C2H6 by gas phase electron diffraction - binding effects

Experimental differential cross sections for 40 keV electrons scattered by C₂H₂, C₂H₄ and C₂H₆ molecules were measured using the gas electron diffraction method in the range of the scattering variable s from s = 1 A^?1 to s = 30 A^?1. The differential cross sections for neon were also measured and compared with calculated differential cross sections to calibrate the diffractograph. Experimental differential cross sections show significant deviations with respect to theoretical differential cross sections calculated from the Debye-Ehrenfest model, mainly in the range of small scattering angles. The observed differences are connected to chemical binding effects. From the experimental data, an estimation of the binding energy was carried out. The deduced values: ?0.58 ± 0.20 au for C₂H₂, ?0.94 ± 0.30 au for C₂H₄ and ?1.23 ± 0.40 au for C₂H₆ are in agreement with those obtained by thermochemical methods.     

Preparation and crystal structure of [Bi3I(C4H8O3H2)2(C4H8O3H)5]2Bi8I30 containing the novel polynuclear [Bi8I30] anion

Preparation and crystal structure of the novel compound [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]₂Bi₈I₃₀ are reported. The title compound is prepared by heating of BiI₃ and diethylene glycol at 413 K in a sealed quartz glass tube filled with argon. Deep red single crystals are grown and applied to perform X-ray powder diffraction and X-ray single-crystal diffraction measurements. The compound crystallizes triclinic with space group P-1: Z=2, a=13.217(1) Å, b=15.277(1) Å, c=22.498(1) Å, α=84.33(1), β=73.18(1), γ=67.48(1). [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]₂Bi₈I₃₀ comprises the novel polynuclear [Bi₈I₃₀]⁶⁻ anion and [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]³⁺ as the cation. Cation as well as the anion can be assumed to represent intermediates between solid BiI₃ and BiI₃ completely dissolved in diethylene glycol.     

通过核独立化学位移(NICS)计算研究二价三、五、七元环C2H2M, C4H4M and C6H6M(M=C, Si, Ge, Sn and Pb)的芳香族特性

The aromatic character of divalent three, five and seven-membered rings C₂H₂M, C₄H₄M and C₆H₆M(M=C, Si, Ge, Sn and Pb) is investigated through magnetic and geometric criteria by Density Functional Theory (DFT)method using 6^-311++G(3df,2p) basis set of the GAUSSIAN 98 program. The result of Nucleus-independent Chemical Shifts (NICS)(0.5) calculations show an aromatic character for singlet state of C₂H₂M(M=C, Si, Ge, Sn and Sn) and nonaromatic character for triplet states of C₂H₂M(except M=Ge and Pb). NICS (0.5) calculations show nonaromatic character for the singlet state of C₄H₄C and antiaromatic character for C₄H₄M(M=Si, Ge, Sn and Pb). In contrast, NICS (0.5) calculations indicate antiaromatic character for the triplet state of C₄H₄C and nonaromatic character to C₄H₄M(M=Si, Ge, Sn and Pb). NICS (0.5) calculations show a slightly homoaromatic character for the singlet state of C₆H₆M and anti-aromatic character for triplet state of C₆H₆M.     

Condensation reaction of C4H4 with pyridine

C₄H₄⁺ reacts with pyridine (C₅H₅N) via the channels of proton transfer, charge transfer and condensation with H-elimination. The condensation reaction is of general interest in terms of basic chemistry and is the focus of the present study. By means of theoretical calculations and Fourier transform mass spectrometer experiments using deuterated pyridine and substituted pyridines, the structure of the product ion and the reaction pathways are investigated. From the experimental results we find that the H atom that is eliminated can originate from either pyridine or C₄H₄⁺. The experiments show that elimination of an H atom from C₄H₄⁺ is preferred and that there is an observable kinetic isotope effect. By replacing H atoms with methyl groups in ortho positions of pyridine, the experimental results also suggest possible steric blocking to the condensation. Based on the experimental observations and results of theoretical calculations of several possible structures of intermediates, transition states, and final product ions, a possible reaction scheme for the condensation-H-elimination is discussed.     

Reactions of C2(a 3πu) with CH4, C2H2, C2H4, C2H6, and O2 using multiphoton UV excimer laser photolysis

C₂(a ³π_u) disappearance rate constants of 1.44, 0.96, 0.0296, 0.0130 and < 10^?6(x10^?10cm³s^?1) are reported for reactions with C₂H₄, C₂H₂, O₂, C₂H₆, and CH₄, respectively at 298 K. C₂(a ³π_u) fragments are generated by multiphoton ArF excimer laser photodissociation at C₂H₂, and monitored by dye laser induced fluorescence. Arguments are presented which favor chemical reactions over the C₂(a ³π_u) → (X ¹σ⁺_g) quenching channel. C₂ + C₂H₂ represents the one possible exception to the reactive channel.     

C3H8 separation from CH4 and H2 using a synthesized PDMS membrane: Experimental and neural network modeling

A polydimethylsiloxane (PDMS) membrane was synthesized and permeation behavior of ternary gas mixtures including C₃H₈, CH₄ and H₂ through it was studied as a function of operating parameters. Mixed gas permeability values were also compared with pure gas data as well as literature to validate experimental results. The aim was to predict separation factor (SF) of C₃H₈ as a function of feed temperature, pressure, flow rate and C₃H₈ concentration with the aid of artificial neural network (ANN) technique. Multilayer perceptron (MLP), which is the most common type of feedforward neural network (FFNN), was used for prediction. The Levenberg–Marquardt training method was initially employed to train the net. Then, optimum numbers of hidden layers and nodes in each layer were determined. The selected structure (4:4:5:1) was finally used to predict SF of C₃H₈ for different inputs in the domain of training data. The modeling results showed that there is an excellent agreement between the experimental data and the predicted values, with mean absolute errors of less than 1%. Both modeling and experimental results confirmed that increasing feed temperature, feed pressure and C₃H₈ concentration in feed debilitates separation performance; however, SF increases with increasing feed flow rate. As a result, ANN can be recommended for the modeling of mixed gas transport through dense membranes such as PDMS.     

Evidence for the distortion of C2H4 and C2H2 chemisorbed on W(100)

The adsorption of C₂H₄ on W(100) has been studied by ultraviolet photoelectron spectroscopy with hν = 21.22 eV. The spectrum measured after in initial saturation exposure at 80 K exhibits structure which correlates well with energy levels recently calculated by Demuth and Eastman (DE) for sp³ rehybridized C₂H₄. Dehydrogenation of the adsorbate, either by subsequent heating to 295 K or direct adsorption at 295 K, yields a spectrum which correlates with DE's calculation for sp² rehybridized C₂H₂. These results suggest that C₂H₄ and C₂H₂ may be distorted from their planar and linear structures respectively and that the CC bonds on these molecules are stretched by adsorption on W(100). Qualitative arguments suggest that the bonding site for both melecules is directly over a W atom and that the Dewar—Chatt model for πd bonding in organometallic compounds is applicable.     

Hydrothermal synthesis and characterization of a new 3D vanadium(III) phosphite (C4H8N2H4)0.5(C4H8N2H3)[V4(HPO3)7(H2O)3]1.5H2O

A new vanadium(III) phosphite, (C₄H₈N₂H₄)_0.5(C₄H₈N₂H₃)[V₄(HPO₃)₇(H₂O)₃]1.5H₂O, has been synthesized hydrothermally by using V₂O₅, H₃PO₃ as reactants, piperazine as the structure-directing agent. The as-synthesized product was characterized by powder X-ray diffraction, IR spectroscopy, inductively coupled plasma analysis, thermogravimetric analysis, and SQUID magnetometer. Single-crystal X-ray diffraction analysis shows that the title compound crystallized in the trigonal space group (No. 165) with the parameters: , , and Z=4. Its structure is built up by alternation of octahedral VO₆ or VO₅(H₂O) and pseudo-pyramidal HPO₃ units to form infinite 2D layers, and these layers are interconnected by sharing vertex-oxygen with octahedral VO₆ units to generate a 3D open-framework structure with 12-membered ring channels in a and b directions, respectively, where there exist entrapped diprotonated and mono-protonated piperazine cations, and water molecules. Magnetic measurement indicates that paramagnetic behavior is observed down to 4 K.     

Vibrational spectra of cyclooctatetraenyl alkali metal complexes [C8H8M2 (M = Na, K)]: A theoretical study

The cyclooctatetraenyl dianion (C₈H₈²⁻) π-conjugated system forms a stable complex system with alkali and some transition metals. The results of vibrational analysis for C₈H₈M₂ (M = Na, K) complexes were reported here. The geometries of C₈H₈M₂ (M = Na, K) were optimized using ab initio (HF, MP2, CCSD(T)) and DFT (B3LYP) methods with 6-311G** and 6-311++G** basis sets and the harmonic frequencies were obtained. To reproduce and compare with the experimental values the structurally similar molecules C₅H₅M (M = Na, K) and benzene were studied. The scale factors obtained from these systems were applied to predict the experimental frequencies of C₈H₈M₂ (M = Na, K). The force field and vibrational spectra are analyzed and the most probable assignments are proposed for all the fundamentals based on the potential energy distribution.     

Cationic rhodium tetrafluorobenzobarrelene complexes with diolefin or arene ligands,crystal structures of [Rh(TFB)(arene)] ClO4, (arene = C6Me6, C6H3Me3, C6H4Me2)

The preparation and properties of complexes of the general formulae [Rh(TFB)(diolefin)]ClO₄, [Rh(TFB)(arene)]ClO₄ and [Rh(TFB)L₂]ClO₄, (TFB = tetrafluorobenzobarrelene, L = dimethylsulfoxide and tetrahydrothiophen) are described. The crystal structures of the arene complexes (arene = C₆Me₆, C₆H₃Me₃ and C₆H₄Me₂) have been solved by X-ray methods. The three compounds crystallize in quite similar lattices: R3c, a = b = 27.122, 26.233, 25.731 and c = 17.079, 16.388, 16.256 Å, respectively. δR-plots for about 2000 reflections show the agreement in the refinements carried out up to R-values of 5%, 5% and 4% respectively. The Rh atom is coordinated to the double bonds of the TFB and to the arene ring in all three compounds, but the deviation from planarity of the arene and its relative position with respect to the TFB moiety varies.     

Time-dependence of the electron-impact-induced unimolecular decay process C3H8+ → C3H7+ + H

A time-of-flight mass spectrometer has been modified to study directly the time dependence of metastable decay processes by introducing a variable time delay between the ionization and extraction pulses and by providing a set of retarding plates and grids in the flight tube to select a single parent ion species for study and to resolve the peak into parent ion, daughter ion and daughter neutral components. The experimentally determined time dependence of the unimolecular decay process C₃H₈⁺ → C₃H₇⁺ + H is compared with previously published predictions of the quasiequilibrium theory of mass spectra.     

Mass spectra of the thioethers C6F5SC6H4X

The mass spectra of a number of thioethers of the type p-XC₆H₄SC₆F₅ (X = H, Cl, NO₂, SC₆F₅, CO₂C₂H₅, C₆H₅) have been examined. These spectra have been compared with those of (C₆H₅)₂S and (C₆F₅)₂S. Fragmentation patterns have been deduced from metastable peaks. The spectrum of p-ClC₆H₄SC₆F₅ has been studied in more detail.